The present invention relates to an apparatus for slitting a moving web of corrugated paperboard or the like and, more particularly, to a slotted anvil assembly for supporting the running web below and in cooperation with an upper rotary slitting blade.
Apparatus for longitudinally slitting a continuous running web of corrugated paperboard is well known in the art. Such apparatus typically also includes a related mechanism for simultaneously providing longitudinal score lines in the advancing web, which score lines facilitate subsequent folding in the construction of paperboard boxes. Thus, a combined slitter-scorer utilizes pairs of rotatable cutting tools and scoring tools disposed in the path of the running web with one tool of each pair disposed on each side of the web. Typically, multiple slitting tools are mounted coaxially and spaced laterally across the width of the web and, likewise, multiple scoring tools are also coaxially mounted and spaced laterally across the width of the web.
In accordance with the teaching of prior art U.S. Pat. No. 5,090,281, the moving web is directed through a thin circular blade rotating at high speed with the board supported below the blade by a roller assembly in contact with the underside of the web. Each such roller assembly includes a pair of rollers which are rotatably mounted to provide tangent contact with the underside of the web and to define therebetween a slot which is positioned to receive the lower edge of the high speed rotary cutting blade positioned over the web. These supporting rollers are also sometimes referred to as anvil rollers since they support the paperboard web against the cutting force of the thin, high speed slitting blade.
Prior art U.S. Pat. No. 5,197,366 discloses a roller assembly in which the rollers of each pair are mounted on separate rotational axes displaced from one another by a small angle to define a blade-receiving slot which is downwardly divergent. The rollers of each pair are also biased toward one another to cause the axially adjacent radial edge portions of the rollers at the point of supporting web contact to bear against the faces of the blade received in the slot. Contact between the anvil rollers and opposite blade faces also produces a sharp, high quality cut edge in the paperboard web. The angled anvil roller assembly also minimizes the build up of paperboard adhesive on the rollers. It also minimizes the entry of adhesive, board dust and board scraps into the blade-receiving slot between the rollers. Foreign material that enters the slot is also more readily discharged with roller rotation.
However, the foregoing anvil roller assembly is intended for use primarily in a corrugator in which an order change is facilitated by creating a machine direction gap in the web, thereby permitting repositioning of the slitting tools (and scoring tools) without disengaging or moving the tools from their operative cutting orientation. The split anvil roller assembly with the slitting blade positioned in the slot between the rollers permits the latter to be repositioned by driving the slitting blade tool head and carrying the anvil roller assembly therewith. Because the anvil rollers are always engaged with the rotary cutting blade, proper alignment between the blade and rollers is always maintained, even as their cross machine direction position is changed (as during presence of the gap in the web).
In another type of corrugator, order change is effected by moving the cutting tools out of operative slitting position, repositioning the tools in the cross machine direction to the new order position, and then plunging the tools back into the running web. Preferably, the slitter-scorer will have two separate slitting stations (and two separate scoring stations) whereby the inactive slitting station may be set for the new order such that, when the running order slitting tools are moved out of operative slitting engagement at order change, the already positioned slitting tools on the other axis may be simultaneously plunged into slitting contact with the web. A complicating factor in a no gap order change is that the slitting blade and the anvil roller assembly must be repositioned in the cross machine direction independently of one another, and the slitting blade must re-engage the gap in the anvil rollers as it is plunged back into slitting engagement. Because of this independent repositioning, there may be slight position errors between the slitting blade and the anvil roller slot which could interfere with proper re-engagement.
The present invention is directed to a method and apparatus for opening the slot or gap between the anvil rollers to accept the plunging slitting blade, closing the anvil rollers on the blade with an appropriate force, and permitting the anvil rollers to float in the cross machine direction to self-align with the blade.
In an alternate embodiment, the anvil rollers are replaced by a pair of anvil plates that are mounted to define the slot between adjacent plate edges. Opening and closing the slot is effected in the same manner as in the preferred anvil roller embodiment.
Each anvil roller assembly is supported on linear ways extending in the cross machine direction. Each anvil assembly carries a drive motor to move the roller assembly to a commanded position, dictated by the order to be run, and then locked in place. Alternate means for positioning the anvil roller assembly and the cooperating tool head for the slitting blade, such as robotic placement, could also be used. The anvil roller assembly is also supported on a short linear bearing extending in the machine direction that allows adjustment of the position of the anvil rollers to compensate for blade wear. Directly supporting the anvil roller pair is a pivot mechanism having a horizontal pivot axis extending in the machine direction and positioned on the roller assembly center line. This pivot mechanism supports both halves of the roller assembly in a sort of clam shell manner. The two halves of the roller assembly are independently pivotable on the pivot axis and a separate air cylinder joins the two halves to draw them together on cylinder retraction, thereby closing the gap and bringing the upper edges of rollers into contact with the opposite faces of the slitting blade. As the cylinder is retracted and the rollers pinch on the blade, they automatically align themselves with the blade. The clamping air cylinder imposes equal forces on both sides of the blade, as determined by air pressure and the positioning of the cylinder.
When the anvil roller assembly is repositioned in the cross machine direction and in preparation to receive a slitting blade plunged through the running web and into the slot between the rollers, the air cylinder extends to separate the rollers at the blade entry slot. Adjustable stops on the supporting structure limit the gap between the rollers and precisely center the gap to provide an optimum target for the thin rotary cutting blade as it is plunged into the slot.
In accordance with the alternate embodiment, the anvil rollers are replaced by a pair of anvil plates which together define a web supporting surface and have adjacent edges that define the blade receiving slot. Preferably, the anvil plates and the mounting brackets comprise a pair of channel sections each having a lower flange and an upper flange connected by an intermediate web. The pivot joint connects adjacent edges of the lower flanges, and the upper flanges form the anvil plates. The first actuator is mounted to interconnect the webs of the channel sections. The entire lower support arrangement is carried on a base plate to which it is connected by the pivot joint. A stop is provided that extends between each mounting bracket and the base plate to limit movement of the first actuator to open the slot. The stops are preferably adjustable. The base plate is also preferably mounted for movement along a linear track that extends parallel to the direction of web travel. An adjustable lock is provided for selectively adjusting the position of the lower support arrangement along the track and for locking the support arrangement in a selected position.